U.S. Pat. No. 5,127,883 entitled "Homogeneous Speed-variating Means as Eccentrically Operated" also granted to the same applicant of this application discloses a central eccentric wheel carrying two disks, disposed on two opposite sides of the central eccentric wheel, eccentrically rotating about an axle of a bike wheel so that a homogeneous wide speed variation can be effected by a first variation from the first disk to the central eccentric wheel and a second speed variation from the central eccentric wheel to the second disk. However, in adjusting the central eccentric wheel (1) by moving an adjusting pipe (42) of the variable speed adjusting means (4) of the U.S. Pat. No. 5,127,883, the adjusting pipe (42) will be obstructed or retarded by the guiding disk (31) of the chain wheel (3) including the central ring (311) of the guiding disk (31) and the axle, being impossible to adjust a center of the eccentric wheel to align or approximate the axle axis, so that a radial movement of the eccentric shell (1) about the axle (51 ) is still limited to thereby influence its speed-variation effect.